The gasification of granular coal in a fixed bed is described in Ullmanns Encyklopadie der technischen Chemie, 4th edition (1977), vol. 14, pages 383 to 386. Details of the gasification process in which the ash remains solid are apparent from U.S. Pat. No. 3,540,867. That patent refers also to the devolatilization of the coal. The gasification of fine-grained coal in a circulating fluidized bed is described in U.S. Pat. No. 4,347,064.
The gasification and devolatilization of coal result in a formation of condensate, which must be processed. Details of such processing are apparent from German Application No. 25 42 055 and German Pat. No. 25 43 532 and the corresponding U.S. Pat. Nos. 4,031,030 and 4,065,273.
That processing results in the formation of a condensate phase which consists mainly of water but must by no means be discharged into a receiving body of water because it still contains phenols, ammonia, hydrogen sulfide, carbon dioxide and cyanide ions. The further processing of that condensate is explained in Laid-open German application Nos. 22 29 213 and 25 27 985 and in the corresponding U.S. Pat. Nos. 3,972,693 and 4,060,591. Details of that processing are also apparent from an article in "Chemsa", May 1979, pages 71 to 73.
The water obtained by the treatment of the condensate by known processes is only slightly contaminated but still contains cyanide ions. Such water has previously been delivered to a biological sewage purifying plant. But it has been found that difficulties arise also in such a plant owing to the toxicity of the cyanide ions.